The invention relates to a radius marrow nail which did not previously exist in the form proposed.
Bone fractures in the vicinity of the wrist joint occur relatively frequently. Especially in older persons the feeling for one""s equilibrium becomes poorer, the hands are used more for support and at the same time a weakening of the bones takes place. The result is fractures of the radius bone in the vicinity of the articular surfaces to the wrist joint, i.e. to the scaphoid and to the lunate bone. These fractures arise as shearing beneath the articular surfaces or pass transversely through the articular surfaces. The previous treatment methods consisted in the application of bone plates and/or bone screws or in the application of a plaster cast with the risk that the bone fragments do not exactly grow together in an ideal position.
It is an object of the invention to create a reliable splinting for fractures of the radius bone in the vicinity of the wrist joint. This object is satisfied by a radius marrow nail having a curvature of its longitudinal axis corresponding to an average radius of curvature 100 less than R less than 1000 mm, having a securing head for an aiming device and having an inclined transverse bore which crosses the longitudinal axis at a distance of less than 30 mm from the end of the securing head.
The advantage of this marrow nail lies in that it can be introduced outside the articular surface for the scaphoid at the styloid process and permits the introduction of a bone screw for fixing and securing directly beneath the articular surfaces in the region of the greatest transverse extent. In this the marrow nail which is anchored in the radius bone serves as a reference for the bone fragments to be secured. A further advantage lies in that through the splinting from within only minor external lesions need be made for the entry of marrow nails and for securing screws.
In accordance with aspects of the present invention, it is advantageous to provide radius marrow nails of different lengths with lengths of from 50 to 200 mm and with different diameters of from 3 to 10 mm in order to cover the spectrum of different patients. In order not to unnecessarily weaken the securing head for the securing of a hammering-in and aiming apparatus and for the provision of the inclined transverse bore, it is provided with a larger outer diameter than the rest of the radius marrow nail. The transverse bore can form an angle a between 40xc2x0 and 70xc2x0 with the shaft axis of the securing head in order to cross a region close beneath the joint sockets in the distal region of the radius bone with the transverse bore and in order also to grip bone fragments of fractures through the joint sockets. With an angle a between 55xc2x0 and 65xc2x0 the transverse bore can be displaced distally to such an extent that its longitudinal axis crosses the securing head at a distance of less than 15 mm ahead of its end. A further transverse bore for anchoring the radius marrow nail is provided in its tip. Body-compatible metals, for example chromium-cobalt-nickel alloys in accordance with ISO 5832-1, or titanium alloys, are suitable as material for the radius marrow nail. For introducing the marrow nail an awl, of which the frontal region corresponds to the radius marrow nail with respect to its outer diameter and the curvature of its longitudinal axis, is first applied in the vicinity of the styloid process in order to open the marrow nail in the form of a long extended curvature. This has the advantage that the actual articular surfaces to the scaphoid and to the lunatum remain untouched. Then the radius marrow nail can be driven in at its securing head into the radius bone with a sliding hammer. For the securing of the sliding hammer the same thread in the securing head can be used as for an aiming bow which is placed on afterwards. Between the aiming bow and the securing head there is additionally a form-fitted coupling which ensures that transverse bores of the radius marrow nail and associated aiming bores in the aiming bow are aligned with one another. The aiming device and the sliding hammer can also be combined with one another.
Since the transverse bores in the radius marrow nail can have a diameter of only a few millimeters, it is advantageous to bridge over the distance between the aiming bow and the transverse bore with a bore sleeve which is resistant to bending. At the same time a borer receives in this way a substantially longer and more precise guiding, which can amount to more than eight times the diameter of the borer. The bore sleeves are removable in order that they do not hinder the securing of the aiming bow and can be driven forwards after its securing to such an extent that they receive a support in the radius bone with their sharpened front edge.
The invention will be described in the following with reference to exemplary embodiment.